Today, signal processing is performed on a wide range of computer systems. The range of signal types processed by such computer systems include audio signals. The source of these audio signals could be a microphone, a sound playback machine, etc. The processing of these audio signals is usually accomplished using a separate signal processing chip. The signal processing chips operate on the audio signals through the use of audio data converters, which receive the audio signals and put them in a form upon which the signal processing chip can operate.
Audio data converters typically only serve the function of providing conversions from an audio signal format into a bit format on which the signal processing chips on a computer system can act. Additional functions such as output gain, input gain, muting, filtering, and sample rate selection are usually performed using external circuitry and not the audio data converters. Other functions such as overflow protection, error detection, and I/O bit operations are incorporated into some converter chips of the prior art. Typically, the reason for the exclusion of the additional functions on the converter chips is due to the fact that the converter chips are expensive in themselves and additional features would only add to their overall expense.
The transfer of data between the converter chips and the signal processing chips is usually accomplished according to a distributed algorithm, known as a protocol. The protocol interconnects the audio processing system to the audio data converters in a manner which allows each to communicate in a recognizable manner. Thus, the protocol allows the audio processing system and the audio data converters to interact in a cohesive way.
When data is transferred between the audio data converters and the audio processing system, data is typically transferred between ports on the audio processing chip and on the audio data converter chip. One prior art technique for transferring data between the audio data converters and the audio processing system involves the use of two separate serial ports. One of the serial ports is used for transfers of data in the form of a bitstream. The other serial port is used for sending control signals to the external circuitry which would perform output and input gain, muting, filtering, and sample rate selection, etc., since these functions are not typically performed by the audio converter chips. Information indicating the status of these operations would be returned on this serial port from the external circuitry. Thus, the control and status information are transferred on the second serial port coupled between the audio processing chip and external circuitry. Another prior art method also uses a serial port for transferring audio data. However, one or more parallel ports are also employed to provide parallel bits (i.e., pins on the package) for manipulating some external functions.
Another prior art method of transferring data between audio converters and the audio processing system is the AES/EBU protocol. The AES/EBU protocol interconnects digital audio devices using a serial port. Some of the bits in the bit stream transferred on the serial port contain status information. This information usually involves error correction and mode, but not control information. Furthermore, the AES/EBU protocol is utilized for interconnecting equipment to equipment in a uni-directional interface, such that the information is only transferred one direction.
One problem with prior art protocols is that when sending control information, bits have fixed meanings. That is, a separate bit (or bits) is either set or not in the serial bit stream to indicate to the device receiving the control information what functions are to be performed. If output gain control is desired, a particular bit is set. Similarly, if a muting is desired, a different bit is set. The same fixed bit format is used when requesting status information. Depending on what status information is required, a particular bit in the serial bit stream is set. This type of fixed bit format only supports a limited range of devices. As long as the control and status information is understood by a device, then it can use the protocol. Any other devices wishing to employ the protocol are limited to communicating the same control and status information. A device having additional functions or status available could not use the fixed bit format to access the additional information or provide the additional control. Additional control and status information not supported by the protocol would be transmitted through other means, such as additional pins. However, many different devices utilize a wide range of control functions. Therefore, many extra pins or other hardware would be required to allow all of the control and status information to be transmitted between devices. These additional required hardware devices can increase the cost and complexity of the system, which system designers and manufacturers wish to avoid. Thus, it is desirable to provide a protocol that is flexible enough to support a variety of devices to communicate control and status information specific to the devices employing the protocol, while not increasing the complexity of the protocol or the system.
As will be shown, the present invention involves a protocol for transferring data between an audio digital processing system and an audio data converter system. The protocol includes the transferring of multiplexed digital audio data and control/status information serially. Thus, protocol of the present invention transfers digital audio and control/status information serially on the same interconnection between the audio signal processing and audio data converters of a computer sound subsystem.